Addition-curable silicone gel composition

ABSTRACT

A silicone gel composition is characterized by excellent storage stability in a non-cured state and by high adhesion to a substrate and long-term stability of consistency at elevated temperatures after curing. The silicone gel composition comprises: a polyorganosiloxane (A), which consists of polyorganosiloxane (A-1) that contains R(CH 3 ) 2 SiO 2/2  units, RsiO 3/2  units R(CH 3 ) 2 SiO 1/2  units, and polydiorganosiloxane (A-2) that contains R(CH 3 ) 2 SiO 2/2  units and R(CH 3 ) 2 SiO 1/2  units, and R(CH 3 ) which contains in one molecule two silicon-bonded hydrogen atoms; an addition-reaction platinum catalyst (C); an organosilicon compound (D) selected from silane of the general formula (R 1 O) n SiR 2   4-n  or a partially hydrolyzed condensate thereof; and an organic titanium compound (E).

TECHNICAL FIELD

The present invention relates to an addition-curable silicone gelcomposition, in particular, to a silicone gel composition which ischaracterized by high storage stability, improved adhesion to asubstrate in a cured state, and capability of forming a silicone gelhaving consistency stable over a long period of time and under anelevated environmental temperature.

BACKGROUND ART

Due to good stress-relaxation, electrical, heat-resistant, and weatherproof properties of cured compounds produced from silicone gelcompositions, these compositions find wide application for preparationof fillers and sealants used in electric and electronic devices. Anexample of such a silicone gel composition is the one having abranch-structured polyorganosiloxane having a molecular terminal cappedwith a silicon-bonded vinyl group, a polydiorganosiloxane having bothmolecular terminals capped with silicon-bonded vinyl groups, apolyorganosiloxane having silicon-bonded hydrogen atoms only on bothmolecular terminals, and a platinum catalyst (see Japanese PatentApplication Publication No. Sho 62-181357).

However, a silicone gel obtained by curing the aforementionedcomposition has poor adhesion to a substrate and can be easily peeledoff from the substrate under the effect of heat cycles and physicalstress. It has been proposed to overcome the above drawback by using asilicone gel composition improved either by adding siloxane units havingalkoxy or epoxy groups to the base polymer or to a cross-linking agent(see Japanese Patent Application Publication No. Hei 4-88060). Anothermethod is based on the use of a silicone gel composition based on theaddition of an aluminum organic compound and an alkoxyalkyl silanecompound to a specific polyorganosiloxane compound (see Japanese PatentApplication Publication No. Hei 6-107947), or on the use of apolyorganosiloxane composition that contains a chain extender having inone molecule two silicon-bonded hydrogen atoms, a cross-linking agentwith at least three silicon-bonded hydrogen atoms in one molecule, analkylpolysilicate, and an alkyl titanate (see Japanese PatentApplication Publication No. Hei 7-233326).

However, improvement achieved in thermal stability and in adhesion of asilicone gel obtained by curing the above composition to a substrate isnot sufficient, and when such silicone gel is maintained over a longperiod of time at relatively high temperatures that exceed 180° C., itbegins to lose its consistency, i.e., becomes harder, can easily bepeeled off the substrate, and forms “cracks” in the gel. Furthermore, ifa silicone gel composition contains an organoaluminum compound,long-term storage of this composition prior to curing causesprecipitation and separation of the organoaluminum compound.

DISCLOSURE OF INVENTION

The inventors carried out a study aimed at the solution of the problemsassociated with this technique. As a result of this study, they arrivedat the present invention. More specifically, it is an object of thepresent invention to provide a silicone gel composition, which ischaracterized by excellent storage stability in a non-cured state and bystrong adhesion to a substrate and by long-term stability of consistencyat elevated temperatures after curing.

The present invention provides a silicone gel composition whichcomprises:

100 parts by weight of a polyorganosiloxane (A), which has a viscosityfrom 10 to 100,000 mPa·s at 25° C. and contains 20 to 100 wt. %polyorganosiloxane (A-1) that contains 80.0 to 99.8 mole % ofR(CH₃)SiO_(2/2) units, 0.1 to 10.0 mole % of RSiO_(3/2) units, and 0.1to 10.0 mole % of R(CH₃)₂SiO_(1/2) units (where R is a monovalenthydrocarbon and where alkenyl groups constitute 0.25 to 4.0 mole % ofthe entire R), and 0 to 80 wt. % polydiorganosiloxane (A-2) thatcontains 90.0 to 99.9 mole % of R(CH₃)SiO_(2/2) units and 0.1 to 10.0mole % of R(CH₃)₂SiO_(1/2) units (where R is a monovalent hydrocarbonand where alkenyl groups constitute 0.25 to 4.0 mole % of the entire R);

a polyorganosiloxane (B), which has a viscosity from 2 to 10,000 mPa·sat 25° C. and contains in one molecule at least two silicon-bondedhydrogen atoms, the aforementioned polyorganosiloxane (B) being used insuch an amount that a mole ratio of silicon-bonded hydrogen atomscontained in this component is within the range of 0.8 to 1.2 relativeto the amount of alkenyl groups in component (A);

an addition-reaction platinum catalyst (C) used in such an amount thatin terms of weight units the metallic platinum constitutes 0.01 to 1000ppm per total weight of components (A) and (B);

0.05 to 20 parts by weight of an organosilicon compound (D) selectedfrom a silane of the general formula (R¹O)_(n)SiR² _(4-n) and apartially hydrolyzed condensate thereof (in the aforementioned formula,R¹ is a alkyl or an alkoxyalkyl group, R² is a substituted ornon-substituted monovalent hydrocarbon group, and “n” is 3 or 4); and

0.001 to 5 parts by weight of an organic titanium compound (E), whereinnone of the polyorganosiloxane, except for component (B), containssilicon-bonded hydrogen atom;

the aforementioned silicone gel composition having a cured-state 1/4consistency, as specified by JIS K 2220, within the range of 10 to 200.

The silicone gel composition of the present invention will be furtherdescribed in more detail.

A polyorganosiloxane (A) is the main component of the composition of theinvention. This component contains 20 to 100 wt. % polyorganosiloxane(A-1) containing R(CH₃)SiO_(2/2) units, RSiO_(3/2) units, andR(CH₃)₂SiO_(1/2) units and 0 to 80 wt. % polydiorganosiloxane (A-2)containing R(CH₃)SiO_(2/2) units and R(CH₃)₂SiO_(1/2) units. If thecontent of constituent (A-1) is less then 20 wt. %, the obtainedcomposition might not cure sufficiently. If necessary, the entirecomponent (A) may consist of constituent (A-1). It is recommended forcomponent (A) to have viscosity of 10 to 100,000 mPa·s. If viscosity isbelow the lower limit of the aforementioned range, the compositioneither will become too fluid in a non-cured state, or will acquireinsufficient physical properties after curing. In case the viscosityexceeds the upper limit, the composition will become difficult to handleand degas during production.

Constituent (A-1) contains R(CH₃)SiO_(2/2), RSiO_(3/2), andR(CH₃)₂SiO_(1/2) units. Constituent (A-1) may contain only theaforementioned three units. If necessary, however, one or two, or morethan two of the following other units can be added to this constituentin small quantities: HO(CH₃)₂SiO_(1/2), RO(CH₃)₂SiO_(1/2),HO(CH₃)SiO_(2/2), and RO(CH₃)SiO_(2/2). In the above formulae, R is amonovalent hydrocarbon that can be represented by methyl, ethyl, propyl,butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, octadecyl or similaralkyl groups; cyclopentyl, cyclohexyl, or similar cycloalkyl groups;phenyl, tolyl, xylyl, naphthyl, or similar aryl groups; benzyl,phenethyl, phenylpropyl, or similar aralkyl groups; 3-chloropropyl,3,3,3-trifluoropropyl, or similar halogenated alkyl groups. Preferableamong these are methyl and phenyl groups. Alkenyl groups shouldconstitute 0.25 to 4.0 mole % of the entire R. If the amount of alkenylgroups in R is below the recommended lower limit, the obtainedcomposition will not possess sufficient curability. If, on the otherhand, the amount of alkenyl group exceeds the upper limit, it would bedifficult to produce a cured body in a gel-like state. The following areexamples of recommended alkenyl groups: a vinyl, allyl, butenyl,pentenyl, or a hexenyl group. Most preferable is a vinyl group.

It is recommended that constituent (A-1) contain 80.0 to 99.8 mole % ofR(CH₃)SiO_(2/2) units, 0.1 to 10.0 mole % of RSiO_(3/2) units, and 0.1to 10.0 mole % of R(CH₃)₂SiO_(1/2) units. If the content of RSiO_(3/2)units is below the lower limit of the recommended range, it would bedifficult to cure the composition to a sufficient degree. If the contentof these units exceeds the upper limit of the range, the obtainedcomposition will become too viscous and will possess low flowability.Although there are no special limitations with regard to viscosity ofconstituent (A-1), it is preferable if viscosity of this constituent iswithin the range of 10 to 10,000 mPa·s.

Constituent (A-2) is a polydiorganosiloxane which containsR(CH₃)SiO_(2/2) units and R(CH₃)₂SiO_(1/2) units. This constituent maycontain only the aforementioned two groups. If necessary, however, oneor two, or more than two of the following other units can be added tothis constituent in small quantities: HO(CH₃)₂SiO_(1/2),RO(CH₃)₂SiO_(1/2), HO(CH₃)SiO_(2/2), and RO(CH₃)SiO_(2/2). In theseformulae, R has the same meaning as defined earlier. It is recommendedthat constituent (A-2) contain 90.0 to 99.9 mole % of R(CH₃)SiO_(2/2)units and 0.1 to 10.0 mole % of R(CH₃)₂SiO_(1/2) units. Although thereare no special limitations with regard to viscosity of constituent(A-2), it is preferable if viscosity of this constituent is within therange of 100 to 100,000 mPa·s.

Polyorganosiloxane of component (B) is used for cross-linking and curingof the composition of the invention into a gel-like substance due tohydrosilation reaction. Component (B) is characterized by having twosilicon-bonded hydrogen atoms in one molecule. If the number ofsilicon-bonded hydrogen atoms in one molecule is less than 2, theobtained silicone gel composition will not possess sufficientcurability, and after curing it could be easily peeled off from asubstrate. If, on the other hand, the number of silicon-bonded hydrogenatoms exceeds 2, the silicone gel obtained after curing the silicone gelcomposition of the invention will have low resistance to heat.

Component (B) may have a linear, partially-branched linear, branched,cyclic, or resin-like molecular structure. Hydrogen atoms can be bondedto silicon at molecular terminals or at sides of the molecular chain.Apart from hydrogen atoms, the following organic groups can be bonded tosilicon atoms in component (B): methyl, ethyl, propyl, butyl, pentyl,hexyl, heptyl, octyl, nonyl, decyl, octadecyl or similar alkyl groups;cyclopentyl, cyclohexyl, or similar cycloalkyl groups; phenyl, tolyl,xylyl, naphthyl, or similar aryl groups; benzyl, phenethyl,phenylpropyl, or similar aralkyl groups; 3-chloropropyl,3,3,3-trifluoropropyl, or similar halogenated alkil groups. Preferableamong these are methyl groups and phenyl groups.

It is recommended for component (B) to have viscosity within the rangeof 2 to 10,000 mPa·s at 25° C. Viscosity at 25° C. below the lower limitwill impair storage stability and handling of the composition underindustrial conditions. On the other hand, if viscosity exceeds the upperlimit, this also will impair handling of the composition during use inthe production process. Component (B) can be represented by a copolymerof a methylhydrogensiloxane and a dimethylsiloxane having both molecularterminals capped with trimethylsiloxy groups, a dimethylpolysiloxanehaving both molecular terminals capped with dimethylhydrogensiloxygroups, a polyorganosiloxane that consists of (CH₃)₃SiO_(1/2), (CH₃)₂HSiO_(1/2), and SiO_(4/2), units, a polyorganosiloxane that consists of(CH₃)₃ SiO_(1/2), (CH₃)₂ HSiO_(1/2), (CH₃)₂ SiO_(2/2), and SiO_(4/2)units, or mixtures of the aforementioned polyorganosiloxanes. Mostpreferable among the above is a dimethylsiloxane having both molecularterminals capped with dimethylhydrogensiloxy groups.

It is recommended that component (B) be used in such an amount that amole ratio of silicon-bonded hydrogen atoms contained in this componentis within the range of 0.8 to 1.2, preferably 0.9 to 1.1, relative tothe amount of silicon-bonded alkenyl groups in component (A). If theaforementioned mole ratio of silicon-bonded hydrogen amounts incomponent (B) to silicon-bonded alkenyl groups in component (A) is belowthe minimal limit of the above range, either the obtained compositionwill not be sufficiently curable and will not exhibit sufficientviscosity during curing, or the silicone gel obtained after curing willnot possess sufficient adhesion to the substrate. In both cases, thesilicone gel obtained after curing will have low thermal stability.

Component (C) is an addition-reaction platinum catalyst intended topromote addition of silicon-bonded hydrogen atoms of component (B) tosilicon-bonded alkenyl groups of component (A). This platinum catalystcan be represented by a platinum black, platinum-carrying activatedcarbon, platinum-carrying fine silica powder, chloroplatinic acid, analcoholic solution of chloroplatinic acid, a platinum-olefin complex, aplatinum-alkenylsiloxane complex, and a fine thermoplastic resin powderthat contains a platinum-type catalyst. The aforementioned thermoplasticresin may comprise a silicone resin, polycarbonate resin, acryl resin,nylon resin, or a polyester resin. It is recommended that theaforementioned resin have a softening point of 5 to 200° C. and havediameter of particles within the range of 0.01 to 10 micrometers.

It is recommended to use component (C) in such an amount that in termsof weight units the metallic platinum constitutes 0.01 to 1000 ppm,preferably 0.1 to 100 ppm, per total weight of components (A) and (B).If the amount is below the lower limit, the obtained composition willnot be sufficiently curable. If the amount of the catalyst exceeds therecommended upper limit, the use of the surplus will not practicallyaccelerate the curing procedure and will not be justifiableeconomically.

Organosilicon compound (D) selected from silane of the general formula(R¹O)_(n)SiR² _(4−n), or a partially hydrolyzed condensate thereof, isneeded for improving adhesion of the silicone gel produced by curing toa substrate. In the aforementioned formula, R¹ is a alkyl or analkoxyalkyl group, R² is a substituted or non-substituted monovalenthydrocarbon group, and “n” is 3 or 4. Alkyl groups designated by R¹ canbe the same or different and can have 1 to 4 carbon atoms. Alkyl groupsare represented by methyl groups, ethyl groups, or propyl groups. Anexample of an alkoxyalkyl group designated by R¹ is methoxyethyl.Monovalent hydrocarbon groups represented by R² can be represented bymethyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl,decyl, octadecyl or similar alkyl groups; cyclopentyl, cyclohexyl, orsimilar cycloalkyl groups; phenyl, tolyl, xylyl, naphthyl, or similararyl groups; benzyl, phenethyl, phenylpropyl, or similar aralkyl groups;3-chloropropyl, 3,3,3-trifluoropropyl, or similar halogenated alkylgroups. Preferable among these are alkyl groups having 1 to 4 carbonatoms, 3,3,3-trifluoropropyl, or phenyl group, but most preferable aremethyl groups.

The aforementioned partially hydrolyzed condensate of silane may have alinear, branched, cyclic, or net-like molecular structure. Furthermore,it can be a monomer or a copolymer. The aforementioned partiallyhydrolyzed condensate of silane can be represented by the followinggeneral formula: (R¹O)_(2 (m+1))Si_(m)O_(m−1), wherein R¹ is the same asdefined above, and m is an integer from 2 to 20. This component shouldhave viscosity of 0.1 mPa·s to 100 mPa·s at 25° C.

It is recommended to use component (D) in an amount of 0.05 to 20 partsby weight, preferably 0.1 to 100 parts by weight, and even morepreferably 0.2 to 2 parts by weight, per 100 parts by weight ofcomponent (A). If component (D) is used in an amount that is below thelower limit, the cured silicone gel will not exhibit sufficient adhesionto the substrate. If the content of component (D) exceeds therecommended upper limit, either the composition will not have storagestability, or the silicone gel obtained after curing will haveunattractive appearance.

Organic titanium compound (E) protects the silicone gel from a decreasein thermal stability, which may be caused by addition of component (D).The following are examples of component (E): tetrabutyl titanate,tetraisopropyl titanate, tetraoctyl titanate, tetraphenyl titanate, or asimilar organic titanic acid ester; diisopropoxy-bis (acetylacetonate)titanium, diisopropoxy-bis (ethylacetoacetate) titanium, or a similarorganic titanium chelate.

It is recommended that component (E) be used in an amount of 0.001 to 5parts by weight, preferably 0.01 to 1 part by weight per 100 parts byweight of component (A). If component (E) is used in an amount less thanthe lower limit of the above range, the silicone gel obtained aftercuring will not acquire sufficient thermal resistance. If component (E)is used in an amount exceeding the recommended upper limit, the obtainedsilicone gel will lose its storage stability.

In order to improve handling of the composition of the invention underindustrial conditions, some additional components can be added to thiscomposition. The following addition reaction inhibitors are examples ofsuch additional components: 3-methyl-1-butyn-3-ol,3,5-dimethyl-1-hexyn-3-ol, 3-phenyl-1-butyn-3-ol, or a similaracetylene-type compound, 3-methyl-3-penten-1-yl,3,5-dimethyl-3-hexen-1-yl, or a similar enyne compound;1,3,5,7-teramethyl-1,3,5,7-tetravinyl cyclotetrasiloxane,1,3,5,7-tetramethyl-1,3,5,7-tetrahexenyl cyclotetrasiloxane, or asimilar cycloalkenyl siloxane; benzotriazole, or a similar triazolecompound. It is recommended that such inhibitors being used in an amountof 0.001 to 5 parts by weight per 100 pats by weight of component (A).

If necessary, the silicone gel composition of the invention can containother additives used in quantities not detrimental to the purposes ofthe present invention. Examples of such additives are the following:dry-process fine silica powder, wet-process fine silica powder, finequartz powder, fine powder of calcium carbonate, fine powder of titaniumdioxide, fine powder of diatomaceous earth, fine powder of aluminumoxide, fine powder of aluminum hydroxide, fine powder of zinc oxide,fine powder of zinc carbonate, or a similar inorganic filler; theaforementioned powdered fillers surface-treated with the followingsubstances: methyltrimethoxysilane, vinyltrimethoxyethoxysilane, or asimilar organoalkoxysilane; trimethylchlorosilane or a similarorganohalosilane; hexamethyldisilazane, or a similar organosilazane;dimethylsiloxane oligomer having both molecular terminals capped withhydroxyl groups, methylphenylsiloxane oligomer having both molecularterminals capped with hydroxyl groups, methylvinylsiloxane oligomerhaving both molecular terminals capped with hydroxyl groups, or similarsiloxane oligomers; higher fatty acids, or their metal salts. Thecomposition of the invention may contain also toluene, xylene, acetone,methylethylketone, methylisobutylketone, hexane, heptane, or a similarorganic solvent; polydimethylsiloxane having both molecular terminalscapped with trimethylsiloxy groups, polymethylphenylsiloxane having bothmolecular terminals capped with trimethylsiloxy groups, or a similarnon-cross-linkable polyorganosiloxane; flame-retarding agents,heat-resistant agents, plasticizers, agents for imparting thixotropicproperties, adhesion enhancing agents, anticorrosive agents, pigments,dyes, fluorescent dyes, etc.

The silicone gel composition of the invention is prepared by uniformlymixing aforementioned components (A) to (E). The silicone gelcomposition of the invention can be stored in the form of two liquidsubcompositions, i.e., a first liquid subcomposition (I) consisting ofcomponents (A), (C), and (E), i.e., without components (B) and (D), anda second liquid subcomposition (II) consisting of components (A), (B)and (D), i.e., without components (C) and (E) {component (A) can bepresent in both liquid mixtures}. Prior to use, the aforementionedliquid subcompositions should be uniformly mixed. If necessary, thesilicone gel composition of the invention can be stored in the form of asingle liquid composition, but storing in the aforementioned two-liquidform provides better protection against curing during storage andagainst deterioration of adhesive properties.

The silicone gel composition of the invention should have a cured-state1/4 consistency, as specified by JIS K 2220, within the range of 10 to200, preferably within the range of 20 to 150. If this characteristic isbelow the lower limit of the above range, the silicone gel obtained fromthe composition will exhibit a decrease in stress-relaxation propertiesand will be prone to formation of “cracks”. If, on the other hand, thecured-state 1/4 consistency exceeds the upper limit of the recommendedrange, the silicone gel will become flowable under the effect ofvibrations.

There are no special limitations with regard to the procedure suitablefor curing the silicone gel composition of the present invention. Forexample, the composition can be poured into an appropriate form orspread over the surface of a substrate as a coating and cured byretaining it at room temperature, or by heating at 50° C. to 200° C.

The silicone gel composition of the invention is normally used as afiller or sealant for electrical and electronic devices of highreliability. In particular, the silicone gel composition of theinvention exhibits excellent adhesion to the materials: gold, silver,copper, nickel, aluminum, or similar metals used for manufacture ofelectrodes; poly-phenylene sulfide (PPS), polybutyleneterephthalate(PBT), or other engineering plastics used for manufacture of cases;epoxy resin, polyimide resin or similar thermosetting resins used formanufacture of printed circuit boards; ceramics such as alumina, aluminanitride, or the like; and substrates from various materials.

BEST MODE FOR CARRYING OUT THE INVENTION

The silicone gel composition of the invention will be described indetail with reference to practical examples. Viscosity given in theseexamples relates to values at 25° C. Furthermore, the following methodswere used for measuring adhesion strength, cured-state 1/4 consistency,and heat-resistant properties of the silicone gel composition of theinvention.

Adhesion Strength of Silicone Gel

A specimen for adhesion strength test was prepared by arranging two100-mm long, 25-mm wide, and 1-mm thick plates parallel to each other,spacing them so that, after filling with the silicone gel composition,the layer formed by the composition was 25 mm long, 10 mm wide, and 1 mmthick, and curing the layer for 60 min. at 70° C. Adhesion strength wasmeasured by stretching the obtained specimen at a rate of 5 mm/min. in adirection perpendicular to the adhered surfaces.

Cured-State 1/4 Consistency

A silicone gel composition was slowly poured into a 50 ml glass flaskand formed into a silicone gel by heating for 1 hour at 70° C.Cured-state 1/4 consistency of the obtained gel was measured inaccordance with the provisions of JIS K 2220.

Thermal Resistance of Silicone Gel

A silicone gel obtained after curing by the method described above wasretained in an oven for 400 hours at 200° C. and then removed and cooledto 25° C. at room temperature. After such treatment, cured-state 1/4consistency of the gel was measured in accordance with the provisions ofJIS K 2220.

Practical Examples 1 to 3, Comparative Example 1 to 7

Components shown in Table 1 (in parts by weight) were uniformly mixedand produced in the form of 10 different silicone gel compositions.These silicone gel compositions were retained intact for 3 days at 5° C.and then checked with regard to storage stability by observing formationof a precipitate. In addition to storage stability, the composition wastested with regard to adhesion strength, cured-state 1/4 consistency,and resistance to heat.

In the attached table, SiH/SiCH═CH₂ is presented in terms of a molenumber of silicon-bonded hydrogen atoms contained in component (b-1)or/and component (b-2) in a ratio to 1 mole of vinyl groups incomponents (a-1), (a-2) or/and (a-3).

Component (a-1) is a polyorganosiloxane (with 0.23 wt. % of vinylgroups) having viscosity 680 mPa·s and consisting of 93.5 mole %(CH₃)₂SiO_(2/2) units, 3.3 mole % CH₃SiO_(3/2) units, 2.3 mole %(CH₃)₃SiO_(1/2) units, and 0.9 mole % (CH₃)₂ (CH₂═CH) SiO_(1/2) units.

Component (a-2) is a 400 mPa·s viscosity dimethylpolysiloxane havingboth molecular terminals capped with dimethylvinylsiloxy groups (0.41wt. % of vinyl groups) and consisting of 98.5 mole % (CH₃)₂SiO_(2/2)units and 1.5 mole % (CH₃)₂ (CH₂═CH) SiO_(1/2) units.

Component (a-3) is a 800 mPa·s viscosity dimethylpolysiloxane havingboth molecular terminals capped with trimethoxysiloxy groups andconsisting of 98.9 mole % (CH₃)₂SiO_(2/2) units and 1.1 mole %(CH₃O)₃SiO_(1/2) units.

Component (b-1) is a 16 mPa·s viscosity dimethylpolysiloxane having bothmolecular terminals capped with dimethylhydrogensiloxy groups (0.13 wt.% content of silicon-bonded hydrogen).

Component (b-2) is a 4 mPa·s viscosity copolymer of amethylhydrogensiloxane and a dimethylsiloxane having both molecularterminals capped with trimethylsiloxy groups (0.78 wt. % content ofsilicon-bonded hydrogen).

Component (c) is a complex of platinum with1,3-divinyl-1,1,3,3-tetramethyldisiloxane with 5 wt. % of metallicplatinum (2.48% content of vinyl groups).

Component (d-1) is an ethylpolysilicate [general molecular formulaSi_(m)O(_(m−1))(OC₂H₅)_(2(m+1)), where an average value of “m” is 5), 40wt % content of SiO₂, viscosity 5 mPa·s].

Component (d-2) is methyltrimethoxysilane.

Component (e-1) is diisopropoxy bis(ethylacetoacetate) titanium.

Component (e-2) is tetrabutyltitanate.

Component (e-3) is aluminum acetylacetonate.

TABLE 1 Practical Examples Comparative Examples 1 2 3 1 2 3 4 5 6 7Composition Component (a-1) 50 100 100 50 50 50 50 50 50 — (partsComponent (a-2) 50 — — 50 25 50 50 50 50 100 by Component (a-3) — — — —25 — — — — — weight) Component (b-1) 9.3 6.5 6.5 9.4 6.3 9.5 9.6 9.7 9.86.3 Component (b-2) — — — — — — — — — 0.6 Component (c) 0.1 0.1 0.1 0.10.1 0.1 0.1 0.1 0.1 0.1 Component (d-1) 0.5 0.5 — — — 0.5 0 0.01 0.5 0.5Component (d-2) — — 0.5 — — — — — — — Component (e-1) 0.02 0.02 — — — —0.02 0.02 — 0.02 Component (e-2) — — 0.02 — — — — — — — Component (e-3)— — — — — 0.05 — — — — SiH/SiCH═CH₂ 0.99 0.99 0.99 1.00 0.99 1.01 1.021.03 1.04 0.81 Adhesive Copper 200 190 175 80 150 200 75 80 180 180Strength Nickel 190 180 185 50 120 160 55 50 130 130 (gf)Polybutyleneterephthalate 175 165 190 40 100 150 45 50 140 140 resinAlumina plate 220 210 215 170 195 210 190 180 195 195 ResistanceCured-state 1/4 60 70 72 60 96 63 64 65 62 70 to consistency in initialheat period Cured-state 1/4 58 68 68 55 20 20 55 58 10 10 consistencyafter 200° C. × 500 hrs Storage Existence of precipitation No No No NoNo Yes No No No No Stability

Thus it has been shown that the gel composition of the present inventionexhibits excellent stability in storage, and the silicone gel obtainedby curing the composition has good adhesion to various substrates andpreserves its cured-state 1/4 consistency over a long period of timeeven under elevated temperatures.

1. A silicone gel composition comprising: (A) 100 parts by weight of apolyorganosiloxane having a viscosity from 10 to 100,000 mPa·s at 25°C., where polyorganosiloxane (A) comprises (i) 20 to 100 wt. %polyorganosiloxane that contains 80.0 to 99.8 mole % of R(CH₃)SiO_(2/2)units, 0.1 to 10.0 mole % of RSiO_(3/2) units, and 0.1 to 10.0 mole % ofR(CH₃)₂SiO_(1/2) units, where R is selected from the group consisting ofmonovalent hydrocarbon groups and alkenyl groups, wherein the alkenylgroups comprise 0.25 to 4.0 mole % of R, and (ii) 0 to 80 wt. %polydiorganosiloxane that contains 90.0 to 99.9 mole % ofR(CH₃)SiO_(2/2) units and 0.1 to 10.0 mole % of R(CH₃)₂SiO_(1/2) units;(B) a polyorganosiloxane that has a viscosity of from 2 to 10,000 mPa·sat 25° C. and contains in one molecule two silicon-bonded hydrogenatoms, said polyorganosiloxane (B) being used in an amount such that amole ratio of silicon-bonded hydrogen atoms contained in component (B)is within the range of 0.8 to 1.2 relative to amount of alkenyl groupsin component (A); (C) a platinum catalyst used in such an amount that interms of weigth units the metallic platinum constitutes 0.01 to 1000 ppmper total weight of components (A) and (B); (D) 0.05 to 20 parts byweight of an organosilicon compound selected from a group consisting ofa silane of the general formula (R¹O)_(n)SiR² _(4-n) and a partiallyhydrolyzed condensate thereof, where R¹ is an alkyl or an alkoxyalkylgroup, R² is a substituted or non-substituted monovalent hydrocarbongroup, and n is 3 or 4; and (E) 0.001 to 5 parts by weight of an organictitanium compound, wherein (B) is the only component that containssilicon-bonded hydrogen atom, said silicone gel composition having acured-state 1/4 consistency within the range of 10 to 200 as specifiedJIS K
 2220. 2. The silicone gel composition as claimed in claim 1wherein component (D) is selected from the group consisting of an alkylsilicate and alkyl polysilicate.
 3. The silicone gel composition asclaimed in claim 1 wherein polyorganosiloxane A(i) further comprises anyone or a combination of the units HO(CH₃)₂SiO_(1/2), RO(CH₃)₂SiO_(1/2),HO(CH₃)SiO_(2/2), and RO(CH₃)SiO_(2/2).
 4. The silicone gel compositionas claimed in claim 1 wherein the monovalent hydrocarbon for R isselected from the group consisting of methyl and phenyl groups.
 5. Thesilicone gel composition as claimed in claim 1 wherein the alkenyl groupis vinyl.
 6. The silicone gel composition as claimed in claim 1 whereinpolydiorganosiloxane A(ii) further comprises any one or a combination ofthe units HO(CH₃)₂SiO_(1/2), RO(CH₃)₂SiO_(1/2), HO(CH₃)SiO_(2/2), andRO(CH₃)SiO_(2/2).
 7. The silicone gel composition as claimed in claim 1wherein component (B) is selected from the group consisting of acopolymer of a methylhydrogensiloxane and a dimethylsiloxane having bothmolecular terminals capped with trimethylsiloxy groups, adimethylpolysiloxane having both molecular terminals capped withdimethylhydrogensiloxy groups, a polyorganosiloxane comprising(CH₃)₃SiO_(1/2), (CH₃)₂ HSiO_(1/2), and SiO_(4/2), units; apolyorganosiloxane comprising (CH₃)₃ SiO_(1/2), (CH₃)₂ HSiO_(1/2),(CH₃)₂ SiO_(2/2), and SiO_(4/2) units mixtures thereof.
 8. The siliconegel composition as claimed in claim 1 wherein the amount of component(B) is such that a mole ratio of silicon-bonded hydrogen atoms containedin this component is within the range of 0.9 to 1.1 relative to theamount of silicon-bonded alkenyl groups in component (A).
 9. Thesilicone gel composition as claimed in claim 1 wherein component (C) isselected from the group consisting of platinum black, platinum-carryingactivated carbon, platinum-carrying fine silica powder, chloroplatinicacid, an alcoholic solution of chloroplatinic acid, a platinum-olefincomplex, a platinum-alkenylsiloxane complex, and a fine thermoplasticresin powder that contains a platinum-type catalyst.
 10. The siliconegel composition as claimed in claim 1 wherein the amount of component(C) is 0.1 to 100 ppm, per total weight of components (A) and (B). 11.The silicone gel composition as claimed in claim 1 wherein the amount oforganosilicon compound (D) is 0.1 to 10 parts by weight per 100 parts byweight of component (A).
 12. The silicone gel composition as claimed inclaim 1 wherein component (E) is selected from the group consisting ofan organic titanic acid ester or an organic titanium chelate.
 13. Thesilicone gel composition as claimed in claim 1 wherein the amount ofcomponent (E) is 0.01 to 1 part by weight per 100 parts by weight ofcomponent (A).
 14. The silicone gel composition as claimed in claim 1further comprising at least one component selected from the groupconsisting of an addition reaction inhibitor, an inorganic filler, anorganic solvent, a non-cross-linkable polyorganosiloxane, aflame-retarding agent, a heat-resistant agent, a plasticizer, an agentfor imparting thixotropic properties, an adhesion enhancing agent, ananticorrosive agent, a pigment, a dye, a fluorescent dye, orcombinations thereof.
 15. The silicone gel composition as claimed inclaim 1 wherein the composition comprises: (I) a first subcompositionconsisting of component (A), component (C), and component (E) and (II) asecond subcomposition consisting of component (A), component (B), andcomponent (D).